Marketable Securities - Summary of Amortized Cost and Fair Value (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Sep. 30, 2019
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 14,271	$ 36,965
Gross Unrealized Losses		(2)
Gross Unrealized Gains	1	6
Fair Value	14,272	36,969
U.S. Treasury securities and obligations of U.S. government agencies
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	6,696	31,863
Gross Unrealized Losses		(2)
Gross Unrealized Gains	1	5
Fair Value	6,697	31,866
Bank certificates of deposits
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	500	750
Fair Value	500	750
Corporate securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	4,519	4,317
Gross Unrealized Gains		1
Fair Value	4,519	4,318
Municipal securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	2,515
Fair Value	2,515
Other debt securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	41	35
Fair Value	$ 41	$ 35

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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